video: add a way to disable automatic stereo conversion

Fixes #2111.

DOCS/interface-changes.rst

@@ -20,6 +20,7 @@ Interface changes
 ::
 
  --- mpv 0.10.0 will be released ---
+    - add --video-stereo-mode=no to disable auto-conversions
     - add --force-seekable, and change default seekability in some cases
     - add vf yadif/vavpp/vdpaupp interlaced-only suboptions
       Also, the option is enabled by default (Except vf_yadif, which has

DOCS/man/options.rst

@@ -655,17 +655,17 @@ Video
     which means the value ``0`` would rotate the video according to the
     rotation metadata.)
 
-``--video-stereo-mode=<mode>``
+``--video-stereo-mode=<no|mode>``
     Set the stereo 3D output mode (default: ``mono``). This is done by inserting
     the ``stereo3d`` conversion filter.
 
+    The pseudo-mode ``no`` disables automatic conversion completely.
+
     The mode ``mono`` is an alias to ``ml``, which refers to the left frame in
     2D. This is the default, which means mpv will try to show 3D movies in 2D,
     instead of the mangled 3D image not intended for consumption (such as
     showing the left and right frame side by side, etc.).
 
-    The pseudo-mode ``none`` disables automatic conversion completely.
-
     Use ``--video-stereo-mode=help`` to list all available modes. Check with
     the ``stereo3d`` filter documentation to see what the names mean. Note that
     some names refer to modes not supported by ``stereo3d`` - these modes can

video/csputils.c

@@ -104,6 +104,7 @@ const struct m_opt_choice_alternatives mp_chroma_names[] = {
 // The numeric index matches the Matroska StereoMode value. If you add entries
 // that don't match Matroska, make sure demux_mkv.c rejects them properly.
 const struct m_opt_choice_alternatives mp_stereo3d_names[] = {
+    {"no",     -1}, // disable/invalid
     {"mono",    0},
     {"sbs2l",   1}, // "side_by_side_left"
     {"ab2r",    2}, // "top_bottom_right"